1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a wide viewing angle in-plane switching mode liquid crystal display device.
2. Discussion of the Related Art
Twisted nematic liquid crystal display devices(hereinafter TN LCDs) having high image quality and low consumption electric power are widely applied to flat panel display devices. TN LCDs, however, have a narrow viewing angle due to refractive anisotropy of liquid crystal molecules. This is because prior to applying voltage, liquid crystal molecules are horizontally aligned relative to the substrate but become nearly vertically aligned relative to the substrate when voltage is applied to a liquid crystal panel.
Recently, in-plane switching mode liquid crystal display devices(hereinafter IPS-LCDs) have been widely studied in which viewing angle characteristic is improved and the liquid crystal molecules are nearly horizontally aligned.
FIG. 1A is a plan view of a unit pixel of a conventional IPS-LCD. As shown in the drawing, a unit pixel region is defined by a gate bus line 1 and a data bus line 2 in which the lines are arranged perpendicularly and/or horizontally in a matrix on a first substrate 10. A common line 3 is arranged parallel to the gate bus line 1 in the pixel region. A thin film transistor(TFT) is formed of a crossing area of the data bus line 2 and the gate bus line 1. As shown in FIG. 1B which is a sectional view taken along line I-Ixe2x80x2 of FIG. 1A, the TFT includes a gate electrode 5, a gate insulator 12, a semiconductor layer 15, a channel layer 16, and source/drain electrode 6. The gate electrode 5 is connected to the gate bus line 1, and the source/drain electrode 6 is connected to the data bus line 2. The gate insulator 12 is formed on the entire surface of the first substrate 10.
A common electrode 9 and a data electrode 8 are formed in the pixel region. The common electrode 9 is formed with the gate electrode 5 and connected to the common line 3. The data electrode 8 is formed with the source/drain electrode 6 and electrically connected to the source/drain electrode 6. Further, a passivation layer 20 and a first alignment layer 23a are deposited on the entire surface of the first substrate 10.
On a second substrate 11, a black matrix 28 is formed to prevent a light leakage which may be generated around TFT, the gate bus line 1, and the data bus line 2. A color filter layer 29, and a second alignment layer 23b are formed on the black matrix 28 in sequence. Also, a liquid crystal layer 30 is formed between the first and second substrates 10, 11. When voltage is not applied to LCD having the above structure, liquid crystal molecules in the liquid crystal layer 30 are aligned according to alignment directions of the first and second alignment layers 23a, 23b, but when voltage is applied between the common electrode 9 and the data electrode 8, the liquid crystal molecules are vertically aligned to extending directions of the common and data electrode. As in the foregoing, since liquid crystal molecules in the liquid crystal layer 30 are switched on the same plane at all times, a grey inversion is not created in the viewing angle directions of up and down direction, and right and left direction.
However, in the conventional LCD having the above structure, an aperature ratio is less than desired because the data electrode and the common electrode are opaque. Also, since a short by coupling the common electrode and said gate bus line in the manufacturing process of the LCD is often generated, the yield goes downed. Further, for the gate insulator and the passivation layer between the data electrode and the common electrode, a high driving voltage for switching liquid crystal molecules is required.
Accordingly, the present invention is directed to an plane switching mode liquid crystal display device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an LCD having a high aperature ratio.
Another object of the present invention is to increase the yield of an LCD.
Additional features and advantages of the present invention will be set forth in the description which follows, and will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure and process particularly pointed out in the written description as well as in the appended claims.
To achieve these an other advantages, and in accordance with the purpose of the present invention, as embodied and broadly described, in a first aspect of the present invention there is provided an in-plane switching mode liquid crystal display device comprising first and second substrates; a plurality of gate and data bus lines defining pixel regions and arranged on said first substrate; a common line formed with said gate bus line; a plurality of thin film transistors formed at respective crossing areas of said gate and data bus lines, gate electrodes of said transistors being connected to said gate bus lines, respectively; a gate insulator having a contact hole on said gate electrodes; a transparent first metal layer including a plurality of first electrodes on said gate insulator; a passivation layer having a contact hole on said transparent first metal layer; and a transparent second metal layer including a plurality of second electrodes on said passivation layer, said second electrodes producing plane electric fields together with said first electrodes.
In another aspect of the present invention, an in-plane switching mode liquid crystal display device comprises first and second substrates; a plurality of gate and data bus lines defining pixel regions and arranged on said first substrate; a common line formed with said gate bus line; a plurality of thin film transistors formed at respective crossing areas of said gate and data bus lines, gate electrodes of said transistors being connected to said gate bus lines, respectively; a gate insulator having a contact hole on said gate electrodes; a transparent first metal layer including a plurality of first electrodes and a transparent second metal layer including a plurality of second electrodes on said gate insulator, said second electrodes producing plane electric fields together with said first electrodes on said gate insulator; and a passivation layer on said common line and said thin film transistors.
In anther aspect of the present invention, a method of forming an in-plane switching mode liquid crystal display device comprises the steps of forming first and second substrates; forming a plurality of gate and data bus lines defining pixel regions and arranged on said first substrate; forming a common line formed with said gate bus line; forming a plurality of thin film transistors formed at respective crossing areas of said gate and data bus lines, gate electrodes of said transistors being connected to said gate bus lines, respectively; forming a gate insulator having a contact hole on said gate electrodes; forming a transparent first metal layer including a plurality of first electrodes on said gate insulator; forming passivation layer having a contact hole on said transparent first metal layer; and forming transparent second metal layer including a plurality of second electrodes on said passivation layer, said second electrodes producing plane electric fields together with said first electrodes.
In a further aspect of the present invention, a method of forming an in-plane switching mode liquid crystal display device comprises the steps of forming first and second substrates; forming a plurality of gate and data bus lines defining pixel regions and arranged on said first substrate; forming a common line formed with said gate bus line; forming a plurality of thin film transistors formed at respective crossing areas of said gate and data bus lines, gate electrodes of said transistors being connected to said gate bus lines, respectively; forming a gate insulator having a contact hole on said gate electrodes; forming a transparent first metal layer including a plurality of first electrodes and a transparent second metal layer including a plurality of second electrodes on said gate insulator, said second electrodes producing plane electric fields together with said first electrodes on said gate insulator; and forming a passivation layer on said common line and said thin film transistors.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.